[Devel] [PATCH RHEL7 COMMIT] ms/block: Check for gaps on front and back merges

[Konstantin Khorenko]

Please consider to release a RK patch for it.

https://readykernel.com/

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 08/31/2017 11:59 AM, Konstantin Khorenko wrote:
> The commit is pushed to "branch-rh7-3.10.0-514.26.1.vz7.35.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
> after rh7-3.10.0-514.26.1.vz7.35.5
> ------>
> commit 36178f3003689a99f0b58b6c12e235186952d9a9
> Author: Maxim Patlasov <mpatlasov at virtuozzo.com>
> Date:   Thu Aug 31 11:59:13 2017 +0300
>
>     ms/block: Check for gaps on front and back merges
>
>     Backport 5e7c4274a70aa2d6f485996d0ca1dad52d0039ca from ml. Before the patch,
>     front merge incorrectly used the same req_gap_to_prev() as back merge.
>     Original patch description:
>
>         block: Check for gaps on front and back merges
>
>         We are checking for gaps to previous bio_vec, which can
>         only detect back merges gaps. Moreover, at the point where
>         we check for a gap, we don't know if we will attempt a back
>         or a front merge. Thus, check for gap to prev in a back merge
>         attempt and check for a gap to next in a front merge attempt.
>
>         Signed-off-by: Jens Axboe <axboe at fb.com>
>         [sagig: Minor rename change]
>         Signed-off-by: Sagi Grimberg <sagig at mellanox.com>
>
>     https://jira.sw.ru/browse/PSBM-70321
>     Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
> ---
>  block/blk-merge.c      | 18 +++++-------------
>  include/linux/blkdev.h | 20 ++++++++++++++++++++
>  2 files changed, 25 insertions(+), 13 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index b0ce46d..0e8b7f2 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -294,6 +294,8 @@ static inline int ll_new_hw_segment(struct request_queue *q,
>  int ll_back_merge_fn(struct request_queue *q, struct request *req,
>  		     struct bio *bio)
>  {
> +	if (req_gap_back_merge(req, bio))
> +		return 0;
>  	if (blk_rq_sectors(req) + bio_sectors(bio) >
>  	    blk_rq_get_max_sectors(req)) {
>  		req->cmd_flags |= REQ_NOMERGE;
> @@ -312,6 +314,8 @@ int ll_back_merge_fn(struct request_queue *q, struct request *req,
>  int ll_front_merge_fn(struct request_queue *q, struct request *req,
>  		      struct bio *bio)
>  {
> +	if (req_gap_front_merge(req, bio))
> +		return 0;
>  	if (blk_rq_sectors(req) + bio_sectors(bio) >
>  	    blk_rq_get_max_sectors(req)) {
>  		req->cmd_flags |= REQ_NOMERGE;
> @@ -338,14 +342,6 @@ static bool req_no_special_merge(struct request *req)
>  	return !q->mq_ops && req->special;
>  }
>
> -static int req_gap_to_prev(struct request *req, struct bio *next)
> -{
> -	struct bio *prev = req->biotail;
> -
> -	return bvec_gap_to_prev(req->q, &prev->bi_io_vec[prev->bi_vcnt - 1],
> -			next->bi_io_vec[0].bv_offset);
> -}
> -
>  static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
>  				struct request *next)
>  {
> @@ -360,7 +356,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
>  	if (req_no_special_merge(req) || req_no_special_merge(next))
>  		return 0;
>
> -	if (req_gap_to_prev(req, next->bio))
> +	if (req_gap_back_merge(req, next->bio))
>  		return 0;
>
>  	/*
> @@ -568,10 +564,6 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
>  	    !blk_write_same_mergeable(rq->bio, bio))
>  		return false;
>
> -	/* Only check gaps if the bio carries data */
> -	if (bio_has_data(bio) && req_gap_to_prev(rq, bio))
> -		return false;
> -
>  	return true;
>  }
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index e1662f9..2b9bc88 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1493,6 +1493,26 @@ static inline bool bvec_gap_to_prev(struct request_queue *q,
>  		((bprv->bv_offset + bprv->bv_len) & queue_virt_boundary(q));
>  }
>
> +static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
> +			 struct bio *next)
> +{
> +	if (!bio_has_data(prev))
> +		return false;
> +
> +	return bvec_gap_to_prev(q, &prev->bi_io_vec[prev->bi_vcnt - 1],
> +				next->bi_io_vec[0].bv_offset);
> +}
> +
> +static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
> +{
> +	return bio_will_gap(req->q, req->biotail, bio);
> +}
> +
> +static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
> +{
> +	return bio_will_gap(req->q, bio, req->bio);
> +}
> +
>  struct work_struct;
>  int kblockd_schedule_work(struct work_struct *work);
>  int kblockd_schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);
> .
>